|
|
||
|
126 RAYS OF POSITIVE ELECTRICITY
cathode rays hit the salt or not. As both these conditions have
a great influence on the rate of production of helium we may regard this source as eliminated. In addition to the preced- ing considerations some of the cathodes have been in almost continuous use for months without any perceptible diminution In the rate of supply of helium.
There Is another possibility which It Is much more difficult
to eliminate by means of physical experiments, though the chemical properties of the inert gases may be thought to make It very improbable; this Is that helium can combine with a large number of elements and that these helium compounds exist as Impurities In the salts of these elements and that these compounds of helium, present as impurities In soluble salts, are also soluble. The fact that helium Is given off by nearly every substance shows that this solid compound or compounds must be extremely widely spread if it is to explain the helium production. They must also possess very special chemical properties in order to explain a large number of cases of which the following Is an example: if we take AgNO3, a salt which will give some helium on bombardment, dissolve it in water, add HC1, we get a precipate of AgCl, now this silver chloride on bombardment will also give helium.
Thus If compounds of helium are present as Impurities
they must be precipitated by the same chemical reactions as precipitate the salts of the element with which they are mixed. It must I think be acknowledged that to explain the production of helium by the dissociation of helium compounds present as impurities obliges us to assign to helium chemical properties of a much more energetic kind than those usually assigned to It. On the other hand there are some effects connected with the appearance of helium which suggest that the source of this gas is not the whole mass of the salt but only a small fraction of it, and which would in fact be more |
||
|
|
||